ping shell script

goncalopp · 07-14-2008, 02:32 PM

Hey,
I'm trying to write a shell script to check when my server goes offline (I'm running it on dsl...). Here's the code:

Code:

ping google.com -i 5 -w 5 > /var/log/tmpcheckconnection 2>&1
grep unknown /var/log/tmpcheckconnection > /var/log/tmpcheckconnection2
grep '0 received' /var/log/tmpcheckconnection >> /var/log/tmpcheckconnection2
if [ -s tmpcheckconnection2 ]
then
date '+Connection Unnavailable at %d/%m/%y, %H:%M:%S' >> /var/log/checkconnection.log
fi

rm /var/log/tmpcheckconnection /var/log/tmpcheckconnection2

The thing is, the file checkconnection.log is never created, even when the ping does not succeed :S Any Ideas? (Yes, I'm running it as root)

Also, I plan on running this with cron, and I've put it on my home folder, though only root has rwx access to it; is that ok, or i should put it in another directory? Maybe I shouldn't use /var/log at all??

weibullguy · 07-14-2008, 03:21 PM

Code:

if [ -s tmpcheckconnection2 ]
then
date '+Connection Unnavailable at %d/%m/%y, %H:%M:%S' >> /var/log/checkconnection.log
fi

Your conditional is checking to see if tmpcheckconnection2 is zero size. Even if the ping is unsuccessful, you will create tmpcheckconnection2 with information (i.e., tmpcheckconnection2 will never be zero size).

Take a look at ping's man page, especially this part

Quote:

If ping does not receive any reply packets at all it will exit with code 1. If a packet count and deadline are both specified, and fewer than count packets are received by the time the deadline has arrived, it will also exit with code 1. On other error it exits with code 2. Otherwise it exits with code 0. This makes it possible to use the exit code to see if a host is alive or not.

Why don't you try to use the exit code from your ping command in the conditional instead of all the temporary files? Something like

Code:

ping -i 5 -w 5
if [ 'x$?' == 'x1' ]; then
     date '+Connection Unnavailable at %d/%m/%y, %H:%M:%S' >> /var/log/checkconnection.log
fi

/var/log is fine for log files...that's what it's for anyway. Depending on how your distro implements cron, there may be /etc/cron.daily, /etc/cron.weekly, etc. directories on your system. Placing the script in one of these directories will cause it to be executed at the appropriate periodicity. Otherwise keeping it in your $HOME is OK too.

williebens · 07-14-2008, 03:25 PM

Hello:

Leaving the file in you home directory should work with cron.
I have this setup:

01 1 23 * * root /home/willie/bin/file.sh

It runs well.
Thanks.
--Willie

goncalopp · 07-14-2008, 04:48 PM

Quote:

Originally Posted by weibullguy

Your conditional is checking to see if tmpcheckconnection2 is zero size. Even if the ping is unsuccessful, you will create tmpcheckconnection2 with information (i.e., tmpcheckconnection2 will never be zero size).

Acording to the bash man page,

Quote:

-s file
True if file exists and has a size greater than zero.

I still can't spot what i'm doing wrong, but checking the exit code is indeed much more elegant! I had no idea you could do that (I know, i'll take the time to fully read a scripting tutorial one of these days...:P )
I guess I'll just leave the script on my home folder, then
many thanks

weibullguy · 07-14-2008, 06:12 PM

Yup, you're right about the -s ... I read it wrong. I wasn't on a Linux box earlier, but I just hacked this together and it seems to work.

Code:

ping -c 5 www.google.com
if [[ $? != 0 ]]; then
    date '+%Y-%m-%d %H:%M:%S Connection Unavailable' >> /var/log/checkconnection.log
else
    date '+%Y-%m-%d %H:%M:%S Connection Available' >> /var/log/checkconnection.log
fi

Gives you a log file that looks like

Code:

2008-07-14 19:09:44 Connection Available
2008-07-14 19:10:11 Connection Available
2008-07-14 19:11:42 Connection Unavailable

chrism01 · 07-14-2008, 11:53 PM

Just make sure tha if you create a file in a certain dir, you then inc that path in the
if [[ -s /path/file ]]
test. The OP doesn't do that, so it'd only work if the script was running in /var/log....